A vehicle typically includes a climate control system which maintains a temperature within a passenger compartment of the vehicle at a comfortable level by providing heating, cooling, and ventilation. Comfort is maintained in the passenger compartment by an integrated mechanism referred to in the art as a heating, ventilation and air conditioning (HVAC) air-handling system. The air-handling system conditions air flowing therethrough and distributes the conditioned air throughout the passenger compartment.
The air-handling system commonly employs a housing having a plurality of conduits and doors for selectively controlling a flow of air to various vents within the passenger compartment of the vehicle, depending on an operating mode selected by a vehicle occupant. Each operating mode includes a preselected percentage of the air originating from a mixing chamber delivered to each of the corresponding vents associated with the selected operating mode. The vents may include panel vents, console vents, front floor vents, rear floor vents, windshield defrost vents, and side window defrost vents, for example.
Doors disposed within the housing may be actuated to control the distribution of the air to each of the desired vents by blocking or opening various conduits disposed within the delivery section. For example, a “panel operating mode” may include the air distributed only to the panel vents and the console vents, a “defrost operating mode” may include the air distributed only to the windshield defrost vents and the side window defrost vents, and a “floor operating mode” may include the air distributed to each of the front floor vents, the rear floor vents, the windshield defrost vents, and the side window defrost vents.
One problem associated with the distribution of the air to each of the vents of the housing relates to differences in a desired volumetric flow rate through each of the vents in the respective operating modes. Because each of the vents receives air from a common mixing chamber of the housing, each conduit coupling the mixing chamber to a corresponding vent must be configured to create a desired pressure drop in the air to provide the desired flow rate through of each of the vents.
One method of controlling the pressure drop is to variably restrict one or more of the conduits based on the selected operating mode. The variable restriction of the conduit may be achieved by actuating one or more doors disposed within the housing to control the pressure and flow rate of the air through each of the conduits.
One problem associated with variably restricting the flow of the air through each independent conduit is especially evident when attempting to control the pressure of the air through a conduit having multiple distinct passageways. For example, it is common for a passageway leading to the windshield defrost vents and a passageway leading to the side window defrost vents to branch from a common defrost conduit due to these vents often being used simultaneously. Air flowing from the mixing chamber flows into the defrost conduit before branching to one or both of the windshield defrost vents and the side window defrost vents.
Based on the desired flow rates for each of the respective vents, in certain operating modes a pressure required in the passageway leading to the windshield defrost vents may differ in comparison to a pressure required at each of the side window defrost vents. For example, when operating in the floor operating mode, the windshield defrost vents may require a duct pressure of about 5 PA to deliver the air out of the windshield defrost vents at a volumetric flow rate of about 30-40 m3/h whereas the side window defrost vents may require a duct pressure of about 175 PA to deliver the air out of the side window defrost vents at the same volumetric flow rate of about 30-40 m3/h. In contrast, when operating in the defrost operating mode, the windshield defrost vents and the side window defrost vents may each require approximately the same duct pressure of about 225 PA to deliver the air out of the windshield defrost vents and the side window defrost vents at their required volumetric flow rates of about 250-325 m3/h and 35-45 m3/h, respectively. Accordingly, the variation in pressure required in each of the respective passageways frustrates an attempt to simultaneously control the pressure within each passageway by actuating the door disposed upstream of the defrost chamber, as an attempt to control the pressure in one of the flow paths will also affect the ability to control the pressure in the other of the flow paths.
This problem is further evident in view of changing performance specifications for the distribution of the air to the various vents of the passenger compartment based on the corresponding operating mode, and especially changing specifications related to the relative percentage of the air delivered to the side window defrost vents during the floor operating mode, the defrost operating mode, and a mixed floor/defrost operating mode.
For example, in traditional air handling systems the floor operating mode may be configured to provide about 75% of the air to the floor vents, about 17% of the air to the windshield defrost vents, and about 8% of the air to the side window defrost vents. The traditional mixed floor/defrost operating mode may be configured to provide about 56% of the air to the floor vents, about 34% of the air to the windshield defrost vents, and about 10% of the air delivered to the side window defrost vents. The traditional defrost operating mode may provide none of the air to the floor vents, about 80% of the air to the windshield defrost vents, and about 20% of the air to the side window defrost vents. Thus, the relative percentage of the air provided to the side window defrost vents ranges from 8% to 20%, of the total flow of air, depending on the operating mode.
In contrast, performance specifications for newer air distribution systems require the volumetric flow rate of the air provided to the side window defrost vents to be increased and remain relatively constant across the floor operating mode, the mixed floor/defrost operating mode, and the defrost operating mode.
For example, the new specifications for air distribution during the floor operating mode may require about 72% of the air delivered to the floor vents, about 10% of the air delivered to the windshield defrost vents, and about 18% of the air delivered to the side window defrost vents. The new specifications for the mixed floor/defrost operating mode may require about 56% of the air delivered to the floor vents, about 30% of the air delivered to the windshield defrost vents, and about 14% of the air delivered to the side window defrost vents. The new specifications for the defrost operating mode may include none of the air delivered to the floor vents, about 80% of the air delivered to the windshield defrost vents, and about 20% of the air delivered to the side window defrost vents. Thus, the relative percentage of the air provided to the side widow defrost vents ranges from 14% to 20% of the total flow of the air, depending on the operating mode.
Accordingly, in contrast to the traditional requirements wherein the percentage and/or volume of the air distributed to the side window defrost vents more than doubled from the floor operating mode to the defrost mode, the new specifications require the percentage and/or volume of the air distributed to the side window defrost vents to remain relatively constant throughout all three of the operating modes including a side window defrost function. This relationship presents a situation wherein the pressure at the outlets of the side window defrost vents must remain substantially constant for all three operating modes whereas the pressure at the outlets of the windshield defrost vents must vary significantly depending on the selected operating mode.
One solution to the differing pressure requirements between the windshield defrost vents and the side window defrost vents is to provide a separate door for controlling entry into each flow path branching from the defrost chamber. However, this solution may require the addition of multiple components such as doors, actuators, links, or control elements, thereby increasing a cost and complexity to manufacture the air handling system.
Accordingly, there exists a need in the art for a means of providing a first variable flow of air to a first passageway of a conduit and a second variable flow of air to a second passageway of the conduit using a single flow-control mechanism, wherein the first variable flow of air remains relatively constant compared to the second variable flow of air.